# 递归
# def sum(num):
#     if num > 1:
#         return sum(num - 1) + num
#     else: return num
# print(sum(3))
# def function(n):  #num:第n项
#     if n == 1 : return 1
#     elif n == 2 : return 1
#     else: return function(n-1)+function(n-2)
# print(function(3))
